The present invention relates generally to a method of producing a microstructure bearing composite article that exhibits superior tip deformation resistance qualities. More particularly, the present invention relates to a method of reducing groove tip impression in a brightness enhancement film, in which the key geometrical features of useful brightness enhancement film articles are disclosed.
The use of the microstructure bearing article as a brightness enhancement film is shown in Whitehead, U.S. Pat. No. 4,542,449. One example of a microstructure bearing article, which is useful as a brightness enhancement film, is described in Lu et al., U.S. Pat. No. 5,175,030, and Lu, U.S. Pat. No. 5,183,597. These patents disclose microstructure bearing composite plastic articles and a method of molding the microstructure bearing composite plastic articles. The Lu et al. patent and the Lu patent address forming the microstructure with desired optical properties, such as total internal reflection.
Microstructure bearing articles are made in a variety of forms. One such form includes a series of alternating tips and grooves. One example of such a form is brightness enhancement film, which has a regular repeating pattern of symmetrical tips and grooves. Other examples include patterns in which the tips and grooves are not symmetrical and in which the size, orientation, or distance between the tips and grooves is not uniform.
One major draw back of prior art radiation cured brightness enhancement films is that dark spots were occasionally seen in prior art brightness enhancement films. While the dark spots do not affect the measured brightness enhancement of the product, the dark spots are undesirable because the spots detrimentally affect the cosmetic appearance of the brightness enhancement film. As a result, manufacturers of displays desire brightness enhancement films that do not have such dark spots.
Prior art brightness enhancement films include "Brightness Enhancement Film", a version made from polycarbonate thermoplastic, sold by Minnesota Mining and Manufacturing Company, St. Paul, Minn. and "DIAART" a version made of a radiation cured microstructured layer on a polyester base, sold by Mitsubishi Rayon, Tokyo, Japan.